Wait for and return any notifications that return within timeout

Once you subscribe to notifications with LISTEN, use this to wait for responses on each channel.

Usage

postgresWaitForNotify(conn, timeout = 1)

Arguments

conn: a PqConnection object, produced by DBI::dbConnect()
timeout: How long to wait, in seconds. Default 1

Value

If a notification was available, a list of:

channel: Name of channel
pid: PID of notifying server process
payload: Content of notification

If no notifications are available, return NULL

Examples

library(DBI)
library(callr)

# listen for messages on the grapevine
db_listen <- dbConnect(RPostgres::Postgres())
dbExecute(db_listen, "LISTEN grapevine")
#> [1] 0

# Start another process, which sends a message after a delay
rp <- r_bg(function() {
  library(DBI)
  Sys.sleep(0.3)
  db_notify <- dbConnect(RPostgres::Postgres())
  dbExecute(db_notify, "NOTIFY grapevine, 'psst'")
  dbDisconnect(db_notify)
})

# Sleep until we get the message
n <- NULL
while (is.null(n)) {
  n <- RPostgres::postgresWaitForNotify(db_listen, 60)
}
stopifnot(n$payload == 'psst')

# Tidy up
rp$wait()
dbDisconnect(db_listen)